(a) Field of the Invention
The present invention relates to a method of manufacturing an organic solar cell.
(b) Description of the Related Art
An organic solar cell is a solar cell having a structure which utilizes organic semiconductor materials, including conjugated polymers such as poly(para-phenylene vinylene) (PPV) in which double bonds are alternately disposed, photosensitive low molecular weight compounds such as CuPc, perylene and pentacene, and (6,6)-phenyl-C61-butyric acid methyl ester (PCBM). The organic semiconductor materials can be structurally designed and synthesized into a wide variety, so that organic solar cells have a potential for limitless development.
An organic solar cell such as described above basically has a thin-film type structure, and mainly uses indium tin oxide (ITO), which is a transparent electrode, as an anode and a metal electrode such as aluminum (Al) as a cathode. The photoactive layer has a thickness of about 100 nm and has a bulk heterojunction structure in which a hole acceptor and an electron acceptor exist in mixture.
As the hole acceptor, a conjugated polymer having conductivity, such as PPV, is used, and a fullerene is used as the electron acceptor. At this time, in order to collect, without loss, electrons that have been produced by light at an aluminum electrode through the fullerene, the fullerene should be sufficiently mixed into the conjugated polymer. Therefore, a fullerene derivative such as PCBM can be used so that the fullerene may be thoroughly mixed with the conjugated polymer.
When the conjugated polymer absorbs light, the conjugated polymer produces electron-hole pairs (excitons), and the electrons and holes thus produced are collected respectively at the anode and the cathode via the fullerene and the conjugated polymer, respectively.
Organic solar cells such as described above can be produced in large quantities due to their easy processability and low cost, and can be manufactured into thin films by a roll-to-roll process. Therefore, the organic solar cells described above have an advantage that flexible, large-sized electronic elements can be produced.
However, despite the technical and economical advantages mentioned above, there are still difficulties in putting organic solar cells into practical use because of their low efficiency. Therefore, studies to improve efficiency are being actively carried out in the field of organic solar cells. Studies concerning the efficiency of organic solar cells that have been conducted hitherto are focused on the selection of raw materials or the manufacturing processes for the photoactive layer, the electron transport layer and the hole transport layer so as to effectively utilize absorbed light, as well as the morphology, structure and increased crystallinity of the organic thin films for overcoming low charge mobility.